Aside: Is it true that everyone thought the relational model was too slow to be practicable, until the Oracle team put a very fast implementation together (as Larry Ellison claimed in an interview)?
EDIT according to the article, Oracle had the first commercial version of it, and so from their point of view at the time, I guess it was true. It doesn't say if IBM's release a few weeks later was of comparable speed.
There were academic systems that (a) didn't use the SQL langauge (b) came before Oracle, but wasn't commercialized as quickly as Oracle.
Oracle's biggest business decision was standardizing on IBM's standards, according to Ingres founder Mike Stonebraker. Hugh Darwen and Paul McJones have all had stories about this. One source is: http://www.mcjones.org/System_R/ DB2 was also only funded by IBM on the premise that DB2 would increase disk storage sales: http://www.informationweek.com/news/software/database_apps/s...
EDIT according to the article, Oracle had the first commercial version of it, and so from their point of view at the time, I guess it was true. It doesn't say if IBM's release a few weeks later was of comparable speed.